1. Field of the Invention
The present invention relates to a composite reinforcing material having excellent strength and flexibility for optical fiber cables, the material being produced by composing a particular resin with a fiber reinforcing material.
2. Prior Art
Reinforcing materials for optical fiber cables are known, for example, a composite of a fiber reinforcing material with a thermosetting resin through pultrusion and a composite of a reinforcing material capable of transmitting active ray such as ultraviolet ray with a photo-setting resin through shaping and subsequent curing via ultraviolet ray.
An improved example of the former is disclosed in Japanese Patent Application No. Sho 62-90229, wherein the method comprises coating with a thermoplastic resin a reinforcing material impregnated with a thermosetting resin, thereafter curing the thermosetting resin under heating, and subsequently removing the coated thermoplastic resin. Compared with a routine pultrusion method, the method can increase the production velocity, but requires more complex production equipment and is not suitable for speedy production because additional processes are needed such as coating of a thermoplastic resin and removal thereof after thermosetting.
Alternatively, use has been made of hard and high-strength reinforcing materials for optical fiber cables, including those such as the known examples described above. However, as communications systems have been distributed commonly in company equipment and public equipment and also even into general houses and the cables therefore should essentially be laid out interiorly, a serious problem has occurred in the layout of a known reinforcing material of a high rigidity. In other words, so as to realize wiring in a relatively small interior, use should be made of a reinforcing material, stably exhibiting excellent protective effect when incorporated into a reinforcing component of optical fiber cables, and having a degree of flexibility applicable to curved wiring of a small radius of curvature. Nevertheless, conventional reinforcing materials are generally hard and rigid, lacking flexibility, so that they are defective in interior wiring applicability.
Further, (metha)acrylic resins have been known as a representative active-ray curing resin, but the resins are problematic because they have such a larger polymerization shrinkage that they are poor in the adhesion to fiber reinforcing materials and therefore defective in the reinforcing effect.
Additionally, it cannot be said that the resins are suitable for curved wiring because they are generally hard and fragile. Epoxy resins commonly employed as a resin for composite reinforcing materials are excellent in terms of adhesion to reinforced fibers and flexibility, but the resins are poor in active ray-curability. Therefore, drawbacks have been remarked for the productivity thereof as a composite reinforcing material because of the poor active ray-curability.
Thus, a method has been investigated to improve the desired characteristics described above by a combined use of an epoxy resin and an acrylic resin to exhibit the characteristics of the two in a suitable fashion, and such a composite resin of an ultraviolet ray-curable type is disclosed in Japanese Patent Laid-open No. Hei 4-314721. The composite resin contains an aromatic epoxy resin, an epoxy resin containing both of a cyclohexene oxide group and an alkylene oxide group in the molecule thereof, an acrylate compound and a polymerization initiator at a specific ratio, and is characteristic in that the resin has such a small polymerization shrinkage during curing as well as such a higher curing sensitivity that the resin is readily cured into its depth. Thus, the resin is excellent as a casting resin. However, the resin is not intended for composition with fiber reinforcing materials, and the resin therefore is not satisfactory in terms of adhesion to fiber reinforcing materials and flexibility. Accordingly, it cannot be said that the resin can satisfy the objective of the present invention.